Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$200.32	7.385%	$215.1136	$215.11	$215.10	$215.10
Purchase #2	$232.39	11.146%	$258.2922	$258.29	$258.30	$258.30
Purchase #3	$36.26	8.505%	$39.3439	$39.34	$39.35	$39.30
Purchase #4	$183.33	9.120%	$200.0497	$200.05	$200.05	$200.00
Purchase #5	$224.81	10.746%	$248.9681	$248.97	$248.95	$249.00
Purchase #6	$154.66	5.129%	$162.5925	$162.59	$162.60	$162.60
Purchase #7	$164.53	12.800%	$185.5898	$185.59	$185.60	$185.60
7 purchase totals =	$1,196.30		$1,309.9498	$1,309.94	$1,309.95	$1,309.90